1. Field of the Invention
The present invention relates to a multi-channel optical transmission system, and more particularly, to an apparatus and a method for monitoring each channel performance of a multi-channel optical signal in the multi-channel optical transmission system.
2. Description of the Related Art
An existing multi-channel optical transmission system is operated by a point-to-point transmission method so that multi-channel optical signals are transmitted through the same transmission line in the system. Each of the multi-channel optical signals has identical transmission line characteristics and transmission loss. However, a current multi-channel optical transmission system is changing to a point-to-multipoint transmission which adopts an optical add drop multiplexer and an optical cross connector. In the multi-channel optical transmission system using the point-to-multipoint transmission method, the multi-channel optical signals are coupled/branched in the state of optical signal at each node. That is, since each of the multi-channel optical signals experiences different transmission distances and transmission line characteristics by channels, the optical performance of each channel is not the same. To guarantee the same transmission performance in the multi-channel optical transmission system, each node should have the capability to monitor the performance of the multi-channel optical signals, that is, the intensity, the wavelength and the optical signal-to-noise ratio in the state of optical signal of each channel.
As solutions to monitoring of optical performance by channels in the multi-channel optical transmission system, an arrayed waveguide grating (U.S. Pat. No. 5,986,782), an optical fiber brag grating (U.S. Pat. No. 5,995,255) and a diffraction grating (K. Otsuka, ECOC97, pp. 147-150) are studied. However, the above solutions have limits in measuring the optical signal-to-noise ratio of each channel in a large-capacity multi-channel optical transmission system including the optical add drop multiplexer and the optical cross connector. Especially, the above methods cannot measure the optical signal-to-noise ratio and the wavelength of each channel simultaneously. In addition, in case of an existing optical performance monitoring apparatus using the diffraction grating, the size becomes too large, and the polarization-dependence and the aberration become high when the system is used to obtain the high resolving power used in measuring the optical signal performance.
To solve the above-described problems, it is an object of the present invention to provide an optical signal performance monitoring apparatus in a multi-channel optical transmission system, which has a high resolving power and minimizes an aberration and a polarization-dependence.
It is another object of the present invention to provide a method for monitoring an optical signal performance, which is performed in the optical signal performance monitoring apparatus.
To achieve the above object, an optical signal performance monitoring apparatus in a multi-channel optical transmission system includes:
an optical input unit for controlling the spot size of an inputted multi-channel optical signal and generating the 1st multi-channel beam;
an optical collimation and focusing unit for collimating the 1st multi-channel beam and focusing the 2nd multi-channel beam which is divided by wavelength;
a diffraction and reflection unit for diffracting and reflecting the 1st collimated multi-channel beam, and generating the 2nd multi-channel beam which is divided by wavelength and is in parallel with the 1st collimated multi-channel beam; and
an optical detection unit for measuring the intensity of the 2nd multi-channel beam by wavelength, which is focused by wavelength by the optical collimation and focusing unit.
To achieve another objective, a method for monitoring an optical signal performance in the multi-channel optical transmission system includes:
(a) step of controlling the spot size of an inputted multi-channel optical signal and generating the 1st multi-channel beam;
(b) step of collimating the 1st multi-channel beam;
(c) step of diffracting and reflecting the 1st collimated multi-channel beam, and generating the 2nd multi-channel beam which is divided by wavelength and is in parallel with the 1st collimated multi-channel beam on the same plane; and
(d) step of focusing the 2nd multi-channel beam, measuring the intensity of the 2nd multi-channel beam focused by wavelength, and measuring the optical signal-to-noise ratio by measuring the optical intensity corresponding to each wavelength and an amplified spontaneous emission (ASE) noise strength at the point between optical signals.